[R-390] More Ballast Tube Noise

[Barry Hauser]

I don't know that's such a great bargain.  I have a couple of 3TF4's around,
but never tried them.

There is a document on the Amperite web site which includes the following:

"LIFE EXPECTANCY:
Average life if operated as recommended 2000 hrs.
If operated continuously at maximum voltage 1000 hrs.
If operated continuously at 80% maximum voltage 5000 hrs.
If filament is operated below glow point 5000 hrs. and up

In operation, the Amperite filament starts to glow at one point; as the
voltage is increased, the glow spreads over the entire filament. Like
incandescent lamps, turning the ballast tube on and off reduces its life,
especially if operating near its maximum voltage."
------------------------

So, there's quite a range -- and they recomment operating below the glow
point.  The differential is such that a $9 glowing 3TF4 might not compare
well -- if you need 3 or more of them vs. a 3TF7.

There are some other interesting things in that document, such as:

"GENERAL ADVANTAGES

. Light, compact. No moving parts

. Rugged, will stand vibration of 10G minimum

. Hermetically sealed; not affected by altitude or humidity changes

. Can be changed as easily as a radio tube

. Operates equally well on A.C. or D.C."

Hmmmmm.... hermetically sealed..... 10G's!  ... a bargain at twice the
price.

Finally, that doc also says "It (the ballast tube) consists of a resistance
wire with a positive temperature coefficient of resistance, hermetically
sealed in a bulb containing hydrogen or helium gas."

So, apparently there are von Hindenburg and Non-von-Hindenburg renditions.

You can read the whole thing at http://www.amperite.com/Uploads/Ballasts.pdf

Barry



















----- Original Message ----- 
From: <doorbar61 at tiscali.co.uk>
To: <r-390 at mailman.qth.net>
Sent: Wednesday, February 09, 2005 5:35 PM
Subject: RE: [R-390] More Ballast Tube Noise



hi, just as a matter of interest about 7 weeks ago i purchased on uk ebay
2 3tf4 ballast tubes both are nos for $18 the pair. i put one in my 390a
whicth i use most days and so far it is fine, sure it glows alittle more
red but is this another and cheaper way to keep the 390a running, yours
brian


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